During the course of studies related to the structure and function of parasite (Trypanosoma cruzi) membranes, contamination of a parasite suspension with a motile, rod-like organism, identified as pseudomonas fluorescens, occurred which caused lysis of the flagellates. In view of the potential significance of this observation not only in terms of cellular biology and physiology in general, but more specifically, because of its impact on parasite chemotherpy and/or immunology it was deemed advisable to study this interaction more extensively. Our findings are described in this report.